1. Field of the Invention
The present invention relates to an anti-fogging coating material, an anti-fogging coating (or coating film), and an anti-fogging optical member. Specifically, the present invention relates to an anti-fogging coating material which is coated on a glass base material such as a glass mirror or on a metal base material such as a metal mirror to form a porous film having a large strength and continuously maintaining its anti-fogging properties and also relates to an anti-fogging coating and an anti-fogging optical member using the same.
2. Related Background Art
Transparent base materials such as an inorganic glass have widely been used for optical members such as camera lens and mirrors in the past. However, exposure of such a base material to a high humidity atmosphere may cause condensation on a surface thereof, which may refract and diffuse a light. Therefore, the performance of the optical member will be degraded and the appearance thereof will also be impaired. In particular, a dental mirror, a camera eyepiece and so on, when used, will come into contact with a high humidity atmosphere produced by moisture discharged by breathing or the like and are therefore required to have highly increased anti-fogging properties and persistence thereof. Accordingly, attempts are being made to impart anti-fogging properties to a surface of a base material by providing a coating thereon to make the surface hydrophilic or water-repellent.
Japanese Patent Application Laid-Open No. 11-61029 (corresponding to U.S. Pat. No. 6,306,932) discloses an anti-fogging coating material made by blending at least one selected from inorganic alkoxides, hydrolysates of inorganic alkoxides, and hydrolytic condensation polymers of inorganic alkoxides; polyacrylic acids; and polyvinyl alcohols. However, there has been a problem that the anti-fogging coating thus formed by using such a coating material contains organic polymers and will have a low strength.
On the other hand, Japanese Patent Application Laid-Open No. 55-154351 discloses a hydrophilic thin film which is applied to a surface of a base material in order to impart hydrophilic properties to the surface thereof and characterized by containing at least one of molybdenum oxides and tungsten oxides, and phosphorus oxides. This hydrophilic thin film is also characterized by being applied to a base material through a thin film forming technique such as evaporation, sputtering, ion plating, plasma deposition, or chemical vapor deposition. In addition, Japanese Patent Application Laid-Open No. 54-105120 discloses a method for manufacturing an anti-fogging glass characterized by being manufactured by bringing an inorganic glass into contact with a liquid containing P2O5 or a vapor thereof. However, there has been a problem that the water absorption capacity and the resistance to water of these thin films and anti-fogging glass are insufficient.
Japanese Patent Application Laid-Open No. 9-295835 discloses an anti-fogging thin film characterized in that a thin film formed on a surface of a glass substrate is made into an oxide thin film having a porous structure following a method comprising the steps of preparing a coating solution by using a metal alkoxide compound or a mixed solution of a solution containing dispersed oxide fine particles having a low equilibrium water vapor pressure and a metal alkoxide compound, subjecting the thus obtained solution to hydrolysis and polycondensation reaction in the presence of a solvent, water, an acid and a water-soluble organic polymer; applying the thus obtained coating solution on a surface of a glass substrate and drying the coated substrate; removing the organic polymer by washing with water or a mixed solution of an alcohol and water; and finally baking the coating film at a high temperature. There have been some problems that manufacture of this anti-fogging thin film requires complicated processes and members to which the thin film is applied are limited.
International Publication No. 96/29375 discloses an anti-fogging transparent plate member comprising a transparent base material and a substantially transparent layer containing a photocatalytic semiconductor material, joined to a surface of the base material, wherein the photocatalytic material makes a surface of the layer hydrophilic responding to photoexcitation, thereby allowing the applied condensed water and/or water droplets created by moisture to spread over the surface of the layer so as to prevent the base material from fogging or blurring by the condensed water and/or water droplets created by the moisture. This publication also discloses a method, as one of the methods for forming a layer containing a photocatalytic semiconductor material, in which a suspension containing particles of anatase titania or rutile titania and silica particles is applied to a surface of a base material and sintered at a temperature less than a softening point of the base material.
Japanese Patent Application Laid-Open No. 10-68091 (corresponding to U.S. Pat. No. 6,071,606) discloses a hydrophilic coating characterized in that the hydrophilic coating is a composite film containing titania and an amorphous metal oxide disposed as an outermost layer on a substrate, and that the composite film contains silica and/or alumina particles. This coating contains titania having a photocatalytic activity and is expected to provide the surface with hydrophilic properties by irradiating the surface with a light, however, there remains a problem that contaminants in the air may deposit on the surface when left in a dark place for a long period of time, thereby losing the anti-fogging properties.
As described above, the conventional techniques have been far from satisfying all of the performance requirements such as a film strength, a water absorption capacity, and persistence of the hydrophilic properties, and limited in terms of applications.
It is, therefore, an object of the present invention to solve the above described problems related to the conventional techniques and provide an anti-fogging coating with high hydrophilic properties and high water absorption properties capable of retaining the high hydrophilic properties for a long period of time, an optical member having the anti-fogging coating, and an anti-fogging coating material for forming the anti-fogging coating.
The object of the present invention is achieved by an anti-fogging coating material, comprising a phosphoric acid compound binder; and oxide particles having an average particle diameter of 1 to 300 nm mixed with the phosphoric acid compound binder.
The object of the present invention is also achieved by an anti-fogging coating formed by using the anti-fogging coating material described above.
The object of the present invention is further achieved by an anti-fogging optical member, comprising a base material; and an anti-fogging coating formed on the base material by using the anti-fogging coating material described above.